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Old 06-04-2013, 11:32 AM   #21
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Originally Posted by travelover View Post
Neither of these provide ventilation for the attic space. If you get a ridge vent, make sure they also install soffit vents for incoming air.
Correction! I was wrong about the vents. I have 2 silver "cake box" vents, one on each slope, that just open into the attic with no hoses attached, and one tube type vent on the front slope (sewer vent?). Also, a gable vent in top of the gable. Looks like all are passive. Never hear a fan running. Also, I have lots of soffet vents in the eaves. I was up in the attic 20 years ago, and saw them. Today I rigged up a mirror on a stick and looked around. It looks like my bathroom fan just vents into the attic through a tube that sticks up about 5 feet above the insulation. Using my mirror on the stick I could not find the "sewer vent" or "vent pipe". Will have to get into the attic again somehow, through that small square access hatch ...... ugh...

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Old 06-04-2013, 11:57 AM   #22
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You need to make sure your bath vent doesn't just exhaust directly into the attic, if so you need to finish it through the roof or the soffit. You're adding moisture in the attic whenever you run the bath fan which promotes mold growth. You should check all your soffit vents to make sure they're not clogged with dust, debris and loose insulation. If you decide to do ridge venting, you will need to cover up the gable vent to help promote proper airflow from the soffit to ridge vents. Otherwise, you'll just be pulling air from the gable to the ridge when isn't what you really want to do

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Old 06-04-2013, 12:03 PM   #23
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Ridge vents are fine. They are not functionally any better or worse than standard roof vents placed near the ridge, but some people like the look a bit more.

If a home has standard roof construction (an insulated ceiling over the top inhabited floor with a roof over that), then the attic space definitely needs to be ventilated effectively. That means soffit vents (so air can get in) and vents up high (ridge, gable, "box" etc) so the hot air can get out. This is important in hot climates but also very important in cold climates, else the moisture in the warm air from the home will condense on the cold roof/framing and mold/rot will result. Gable vents can be "okay" for the upper vents, but they often need to be very big in order to get the job done (see math below).

How much ventilation is enough? One rule of thumb is that the Net Free Area (NFA) of the top and soffit vents combined should equal 1:150th of the attic size. The NFA is shown on vents of all kinds and accounts for the obstructive effects of screening, bracing, etc: The NFA can typically be about 1/2 of the actual area of the hole for the vent. So, a 2000 sq foot house would need 2000/150=13.33 sq feet total NFA of soffit and top vents. That's about 6.75 sq feet NFA for top vents and 6.75 sq feet NFA of soffit vents.

Soffit vents: Having vents in the soffits does little/no good if the path of the air is blocked by attic insulation. It is important to have trays installed or take other steps to assure the air can get up into the attic.

Originally Posted by John Galt III View Post
Today I rigged up a mirror on a stick and looked around. It looks like my bathroom fan just vents into the attic through a tube that sticks up about 5 feet above the insulation.
That's a bad setup. Even worse: I've seen clothes dryers vented that way, rather than going outside. Every load of laundry= a gallon or two of water piped up there to the attic to cause mayhem (condense on the roof/truusses in the winter, condense on the ceiling and add to the heating load in the summer). Bathrooms, clothes dryers, stove hoods should all be vented to the outside through a vent in the roof, wall, or (less good but far better than the attic) through a dedicated vent out through the soffit.

For what it's worth.

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